1. Field of the Invention
This invention relates to feeding material into a machine and more particularly to feeding material into a press type machine such as a press brake in such a manner that an operator maintains control over the material being inserted without risk of injury.
2. Description of the Prior Art
It is a common occurrence in modern industry for material in one shape or form to be converted into another shape or form. Many base materials such as aluminum or steel are typically supplied by material vendors in the form of sheet stock. This sheet stock is then processed so that a functional device may be fabricated from the material. The material will be cut, punched, bent, drawn, or squeezed, according to need. Many manufacturing shops accomplish their shape conversion by using presses, machines that supply pressure to accomplish the work required. A particular type press, a press brake, is a machine used for bending, folding, and forming sheet material, by applying pressure.
The press brake presses material between two pieces of a preset die such that the material takes a shape determined by the shape of the die pieces. Typical press brakes have pressure capacities ranging from 25 tons to several thousand tons. These large pressure magnitudes are indicative of the forces applied to the material inserted between the dies to overcome the strength of the material and to firmly form the desired shape.
Most modern press brakes are designed to be manually fed by an operator. The operator holds the material to be shaped with his hands and feeds the material between the die pieces, an area designated as the point of operation. If the material being shaped is small, the operator must place his hands close to the point of operation when holding the material as it is being fed into the machine. The press is then activated and the forces are applied to the material. In some cases the material being held by the operator will tend to move at the holding point as the forces of the dies shape the material. When large forces distort hand-held material in close proximity to the point of operation, a potential hazard exists. Injury to the operator may occur. There exists for many machines, and particularly press brakes, areas designated danger zones, within which a hazard may occur under normal operating conditions. In a press brake, for example, areas where the operator could accidentally jam his hands between the press brake dies or where the bending forces could pin his hands against the brake press structure while he is holding the material, are considered danger zones.
The prior art has developed many approaches to protect a press brake operator in the danger zones. Light beam sensors, for example, have been employed whereby light is directed at the point of operation and the pressing action shut down when a solid element, such as a hand, triggers the device. This method becomes impractical as the material itself can trigger the device.
Pull-out devices have been used whereby the operator's hands are restrained by ropes and are pulled back when the hands approach a specified distance from the point of operation. This device, as it physically withdraws the hands, creates another hazard. Hand injuries can easily result when the hands are forced back while material is turning or twisting in the operator's grip. Furthermore, rope restraints severely limit general operator freedom of motion.
There has also been employed hand-held tongs for gripping the material, some tongs having a universal joint that will pivot when the material is moving during shaping. These tongs have disadvantages in that small pieces become awkward to control and, since the universal joint type tongs can readily pivot, forces required to direct material in the direction of the point of operation are weak.
Therefore, a need exists for a simple, safe approach that can be used by a machine operator when manually feeding material into a machine, and particularly for feeding material into a press type machine such as a press brake.